2024 Volume 12 Issue 2 Article ID: 24-25015
The development of cost-effective, high-performance, and durable cathode catalysts for the oxygen reduction reaction (ORR) is essential for the practical use of microbial fuel cells (MFCs) in organic wastewater treatment. Recently, heteroatom-doped carbon materials have emerged as a promising alternative to platinum as ORR catalysts. In this study, metal-free nitrogen-doped activated carbon catalysts were synthesized through thermal treatment at 1,050°C using urea as an inexpensive nitrogen precursor and commercial powdered activated carbon (AC). The effects of acid and/or alkali washing performed before or after nitrogen doping on the ORR activity of the resulting catalysts were experimentally assessed. The products obtained from the thermal treatment of urea and AC exhibited high ORR activity and contained substantial amounts of pyridine-N and graphitic-N compared to raw AC. Alkali washing was more effective than acid washing, regardless of whether it was performed before or after nitrogen doping. The nitrogendoped activated carbon prepared by washing raw AC with a 1 M potassium hydroxide (KOH) solution before nitrogen doping (KOH–N) exhibited the highest kinetic current density of 3.18 mA/cm2. The kinetic current densities were largely influenced by the pyridinic nitrogen content on the surface of the N-doped ACs. MFCs using air-cathodes with the KOH–N catalyst achieved a maximum power density of 1, 330 ± 60 mW/m2 and a coulombic efficiency of 34.3 ± 6.5%. Pretreating AC with an alkali solution before nitrogen doping is considered an efficient and cost-effective method for producing N-doped AC with high ORR activity.
